Probing Electronic Doping in CVD Graphene Crystals Treated by HNO Vapors.

In this work, we present a comprehensive protocol for achieving hole doping in graphene through exposure to nitric acid (HNO) vapors. We demonstrate gradual p-type surface doping of CVD-grown graphene on a Si/SiO substrate by thermally depositing nitric acid molecules to form self-assembled charge transfer complexes. Detailed analysis of charge carrier concentration and Fermi energy shifts was conducted using Raman, X-ray and ultraviolet photoelectron spectroscopies (XPS/UPS).

Enhanced Raman Scattering in CVD-Grown MoS/Ag Nanoparticle Hybrids.

Surface-Enhanced Raman Spectroscopy (SERS) is a powerful, non-destructive technique for enhancing molecular spectra, first discovered in 1974. This study investigates the enhancement of Raman signals from single- and few-layer molybdenum disulfide (MoS) when interacting with silver nanoparticles. We synthesized a MoS membrane primarily consisting of monolayers and bilayers through a wet chemical vapor deposition method using metal salts.

Biaxial Strain Transfer in Monolayer MoS and WSe Transistor Structures.

Monolayer transition metal dichalcogenides are intensely explored as active materials in 2D material-based devices due to their potential to overcome device size limitations, sub-nanometric thickness, and robust mechanical properties. Considering their large band gap sensitivity to mechanical strain, single-layered TMDs are well-suited for strain-engineered devices. While the impact of various types of mechanical strain on the properties of a variety of TMDs has been studied in the past, TMD-based devices have rarely been studied under mechanical deformations, with uniaxial strain being the most common one.

Biaxial Tensile Strain Enhances Electron Mobility of Monolayer Transition Metal Dichalcogenides.

Strain engineering can modulate the properties of two-dimensional (2D) semiconductors for electronic and optoelectronic applications. Recent theory and experiments have found that uniaxial tensile strain can improve the electron mobility of monolayer MoS, a 2D semiconductor, but the effects of biaxial strain on charge transport are not well characterized in 2D semiconductors. Here, we use biaxial tensile strain on flexible substrates to probe electron transport in monolayer WS and MoS transistors.

Observation of Two-Step Spin Transition in Graphene Oxide-Based Hybrids with Iron(II) 4-amino-1,2,4-triazole Spin Crossover Nanoparticles.

A novel experimental protocol based on a reverse micellar method is presented for the synthesis of graphene oxide (GO)-based hybrids with spin crossover nanoparticles (SCO NPs) of the 1D iron(II) coordination polymer with the formula [Fe(NHtrz)](Br). By introducing different quantities of 0.5% and 1.

Development of Erf-Mediated Craniosynostosis and Pharmacological Amelioration.

ETS2 repressor factor () insufficiency causes craniosynostosis (CRS4) in humans and mice. ERF is an ETS domain transcriptional repressor regulated by Erk1/2 phosphorylation via nucleo-cytoplasmic shuttling. Here, we analyze the onset and development of the craniosynostosis phenotype in an Erf-insufficient mouse model and evaluate the potential of the residual Erf activity augmented by pharmacological compounds to ameliorate the disease.

Observation of two-step spin transition in iron(II) 4-amino-1,2,4-triazole based spin crossover nanoparticles.

A synthetically controllable two-step spin transition was observed in iron(II) spin crossover nanoparticles of the dehydrated one-dimensional coordination polymer [Fe(NHtrz)]Br (NHtrz = 4-amino-1,2,4-triazole) using the reverse micellar method. The change from two-step to one-step hysteretic characteristics succeeded by changing the reaction time.

Structural Defects Modulate Electronic and Nanomechanical Properties of 2D Materials.

Two-dimensional materials such as graphene and molybdenum disulfide are often subject to out-of-plane deformation, but its influence on electronic and nanomechanical properties remains poorly understood. These physical distortions modulate important properties which can be studied by atomic force microscopy and Raman spectroscopic mapping. Herein, we have identified and investigated different geometries of line defects in graphene and molybdenum disulfide such as standing collapsed wrinkles, folded wrinkles, and grain boundaries that exhibit distinct strain and doping.

Efficient Mechanical Stress Transfer in Multilayer Graphene with a Ladder-like Architecture.

We report that few graphene flakes embedded into polymer matrices can be mechanically stretched to relatively large deformation (>1%) in an efficient way by adopting a particular ladder-like morphology consisting of consecutive mono-, bi-, tri-, and four-layer graphene units. In this type of flake architecture, all of the layers adhere to the surrounding polymer inducing similar deformation on the individual graphene layers, preventing interlayer sliding and optimizing the strain transfer efficiency. We have exploited Raman spectroscopy to quantify this effect from a mechanical standpoint.

Mechanical, Electrical, and Thermal Properties of Carbon Nanotube Buckypapers/Epoxy Nanocomposites Produced by Oxidized and Epoxidized Nanotubes.

High volume fraction carbon nanotube (CNT) composites (7.5-16% vol.) were fabricated by the impregnation of CNT buckypapers into epoxy resin.

Spin-Crossover Phenomenon in Microcrystals and Nanoparticles of a [Fe(2-mpz)Ni(CN)] Two-Dimensional Hofmann-Type Polymer: A Detailed Nano-Topographic Study.

The diamagnetic two-dimensional Hofmann-type metal-organic framework [Zn(2-mpz)Ni(CN)] has been successfully synthesized along with its isostructural hysteretic spin-crossover Fe analogue in the form of both bulk microcrystalline powder and nanoparticles. Detailed atomic force microscopy topographic study revealed a nanogrowth relationship between the height and length of the nanoparticle.

Strain Engineering in Highly Wrinkled CVD Graphene/Epoxy Systems.

Chemical vapor deposition (CVD) is regarded as a promising fabrication method for the automated, large-scale, production of graphene and other two-dimensional materials. However, its full commercial exploitation is limited by the presence of structural imperfections such as folds, wrinkles, and even cracks that downgrade its physical and mechanical properties. For example, as shown here by means of Raman spectroscopy, the stress transfer from an epoxy matrix to CVD graphene is on average 30% of that of exfoliated monolayer graphene of over 10 μm in dimensions.

Noncovalent Grafting of a Dy Single-Molecule Magnet onto Chemically Modified Multiwalled Carbon Nanotubes.

While synthetic methods for the grafting of nanoparticles or photoactive molecules onto carbon nanotubes (CNTs) have been developed in the last years, a very limited number of reports have appeared on the grafting of single-molecule magnets (SMMs) onto CNTs. There are many potential causes, mainly focused on the fact that the attachment of molecules on surfaces remains not trivial and their magnetic properties are significantly affected upon attachment. Nevertheless, implementation of this particular type of hybrid material in demanding fields such as spintronic devices makes of utmost importance the investigation of new synthetic protocols for effective grafting.

An Evaluation of Graphene as a Multi-Functional Heating Element for Biomedical Applications.

Graphene has been found to be an excellent heat-conductor due to the high speed of acoustic phonons in its lattice. In this work, we examine in depth a commercial graphene-based waist protector which uses graphene as a heating element. By employing thermal imaging in tandem with Raman microscopy, the thermal characteristics and performance of this device is fully assessed.

Comparison of yields and properties of microbial polyhydroxyalkanoates generated from waste glycerol based substrates.

The accumulation efficiency and the properties of polyhydroxyalkanoates (PHAs) produced from acidified waste glycerol (AWG) and its derivatives via an enriched microbial consortium derived from soil, were investigated in this study. AWG consisted mainly from short chain fatty acids, 1,3 propanediol and residual glycerol, which were also evaluated individually as substrates. Accumulation capacity and yields were estimated after solvent extraction and purification and PHAs were further analyzed in terms of their chemical structure, thermal properties, molecular masses and mechanical properties.

Wrinkled Few-Layer Graphene as Highly Efficient Load Bearer.

Multilayered graphitic materials are not suitable as load-bearers due to their inherent weak interlayer bonding (for example, graphite is a solid lubricant in certain applications). This situation is largely improved when two-dimensional (2D) materials such as a monolayer (SLG) graphene are employed. The downside in these cases is the presence of thermally or mechanically induced wrinkles which are ubiquitous in 2D materials.

Mechanical Stability of Flexible Graphene-Based Displays.

The mechanical behavior of a prototype touch panel display, which consists of two layers of CVD graphene embedded into PET films, is investigated in tension and under contact-stress dynamic loading. In both cases, laser Raman spectroscopy was employed to assess the stress transfer efficiency of the embedded graphene layers. The tensile behavior was found to be governed by the "island-like" microstructure of the CVD graphene, and the stress transfer efficiency was dependent on the size of graphene "islands" but also on the yielding behavior of PET at relatively high strains.

Graphene flakes under controlled biaxial deformation.

Thin membranes, such as monolayer graphene of monoatomic thickness, are bound to exhibit lateral buckling under uniaxial tensile loading that impairs its mechanical behaviour. In this work, we have developed an experimental device to subject 2D materials to controlled equibiaxial strain on supported beams that can be flexed up or down to subject the material to either compression or tension, respectively. Using strain gauges in tandem with Raman spectroscopy measurements, we monitor the G and 2D phonon properties of graphene under biaxial strain and thus extract important information about the uptake of stress under these conditions.

Suspended monolayer graphene under true uniaxial deformation.

2D crystals, such as graphene, exhibit the higher strength and stiffness of any other known man-made or natural material. So far, this assertion has been primarily based on modelling predictions and on bending experiments in combination with pertinent modelling. True uniaxial loading of suspended graphene is not easy to accomplish; however such an experiment is of paramount importance in order to assess the intrinsic properties of graphene without the influence of an underlying substrate.

Deformation of wrinkled graphene.

The deformation of monolayer graphene, produced by chemical vapor deposition (CVD), on a polyester film substrate has been investigated through the use of Raman spectroscopy. It has been found that the microstructure of the CVD graphene consists of a hexagonal array of islands of flat monolayer graphene separated by wrinkled material. During deformation, it was found that the rate of shift of the Raman 2D band wavenumber per unit strain was less than 25% of that of flat flakes of mechanically exfoliated graphene, whereas the rate of band broadening per unit strain was about 75% of that of the exfoliated material.

Stress transfer mechanisms at the submicron level for graphene/polymer systems.

The stress transfer mechanism from a polymer substrate to a nanoinclusion, such as a graphene flake, is of extreme interest for the production of effective nanocomposites. Previous work conducted mainly at the micron scale has shown that the intrinsic mechanism of stress transfer is shear at the interface. However, since the interfacial shear takes its maximum value at the very edge of the nanoinclusion it is of extreme interest to assess the effect of edge integrity upon axial stress transfer at the submicron scale.

Failure processes in embedded monolayer graphene under axial compression.

Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses.

Structural Properties of Chemically Functionalized Carbon Nanotube Thin Films.

Buckypapers are thin sheets of randomly entangled carbon nanotubes, which are highly porous networks. They are strong candidates for a number of applications, such as reinforcing materials for composites. In this work, buckypapers were produced from multiwall carbon nanotubes, pre-treated by two different chemical processes, either an oxidation or an epoxidation reaction.